The invention relates to a process for improving the lightfastness of dyed leathers by the use of alkane or chloroalkane sulfonamides.
Leather is dyed mainly by means of selected acid, substantive and metal-complex dyes and, to a minor extent, basic dyes. In the case of unfinished or just lightly finished leather, the lightfastness of the dye-leather union is a primary criterion of quality. This is so because when a dyed leather is exposed to light, what is measured is the fastness, not of the dyes used but of the dye-leather union.
For this reason, the lightfastness of identical dyes on leather usually is very much inferior to that on textile fibers. The lightfastness of dyes on leather depends in some measure on their structure and on the auxiliary materials used in the manufacture of the leather, such as tanning agents, lubricants, dyeing assistants, etc. (F. Grall and H. Gardere, "Betrachtungen uber die Lichtechtheit des gefarbten Leders" (Reflections on the lightfastness of dyed leather), a paper presented at the 15th IULTCS Congress, Hamburg, 1977; Das Leder 1978, 6, pp. 94 to 98.)
To achieve very good lightfastness, which on leather ranges from 4 to 5, measured in conformity with DIN 54 004, it is by no means enough to use only dyes, tanning agents and lubricants which are stable to light since unpredictable interactions may have a favorable or adverse effect on the lightfastness of the dye-leather union.
The fatliquoring agents used in the particular fatting operation have a decisive effect on the lightfastness of dyed leathers. They influence not only the hue, its depth, brilliance and uniformity, but also the lightfastness of the color imparted. With exacting requirements, so-called "non-yellowing fatliquoring agents" based on sperm oil, neatsfoot oil, synthetic triolein and similar raw materials are therefore used. Synthetic fatting agents based on alkane and chloroalkane sulfonates are regarded as possessing particularly good stability to light. (German patent applications DAS Nos. 1,142,833 and 1,494,828.)
However, for the reasons stated, the desired high lightfastness of the dyed leather, which has a decisive effect on the utility value of leather used in clothing or furniture, of aniline upper leather and suede, etc., is not or not fully achieved regardless of how carefully the auxiliary materials are selected. This is true also when the synthetic fatting agents mentioned are used.
French Pat. No. 866,256 and German Pat. No. 864,905 describe the preparation of sulfonamides by the reaction of chlorine and sulfur dioxide with saturated aliphatic hydrocarbons followed by reaction of the sulfohalides obtained with ammonia or primary and secondary amines. The sulfonamides obtained by this route are suited for use as oiling and fatting agents for materials of fibrous structure and also as lubricants for machinery. It is pointed out that sulfonamides are suited for the fatting and fatliquoring of leather, among other things.
In German Pat. No. 747,403 it is stated that emulsifiers which dissolve clear in mineral oils and fatty oils and exhibit improved effectiveness over long-chain paraffin sulfonates are obtained when these sulfonates are used jointly with sulfonamides, sulfoacylamides or disulfimides prepared by sulfochlorination of long-chain paraffin hydrocarbons followed by treatment with ammonia or its organic derivatives. The clear mixtures of the oils and these emulsifiers are water-soluble and are said to be suitable for use as drilling oils, leather stuffing materials, lubricating and cutting oils.
The use of sulfamides, sulfonamides or sulfimides such as obtained in the reaction of alkane sulfohalides with ammonia or its derivatives, in the fatting of leather in the amounts customary in leather fatting which, depending on the type of the leather and on the composition of the fatting agent, range approximately from 10 to 15 weight percent, based on the shaved weight of the leather, is then described. However, nowhere in the art of record are there any statements to the effect that such products have an effect on the lightfastness of dyed leather, and have such an effect even when used in small amounts.
Because of their insufficient solubility in water, these products cannot, however, be used alone in fatliquoring but must be combined for this purpose with other fatting agents or emulsifiers which assure that the overall combination of the fatting agent is soluble in water or at least gives an emulsion that is sufficiently stable in water.